In the past, incineration was the usual treatment employed for organic waste, specifically, so-called “living matter” including kitchen waste such as leftovers and food scraps (including bones, meat, organs, and vegetable scraps, as well as shells of shellfish and crustaceans), as well as biomass such as lawn, shrub, and tree clippings, chaff, sawdust, and wood chips; however, energy issues and environmental issues that have arisen in recent years now make urgent revaluation of such practices imperative.
In light of these issues, various measures for addressing these urgent problems have been proposed from different quarters, one of the most promising of which is one involving recycling of organic waste. This may involve, for example, reducing organic waste to block, granular, or powder form subsequent to a drying process, and reusing the dried product as organic material such as fertilizer or animal feed.
The use of a drying furnace to obtain such dried products is currently under consideration. Such drying furnaces are typically designed to carry out continuous drying of organic waste by high-temperature treatment through application of heat from outside the furnace to the material being treated, i.e. the organic waste, as the material is progressively transported through the furnace by a screw conveyor or the like.
However, organic waste drying processes such as this have a number of inherent drawbacks, such as: (1) the difficulty in achieving adequate drying; (2) the need for laborious operations to crush or mill the undried waste or dried product into granules or powder of appropriate size in order to reduce its volume; and (3) the final treated product is simply a dried product, and since proteins, carbohydrates, fats, and other nutrients remain present in macromolecular form in such dried products, when the dried product is reused as feed, fertilizer, a soil amendment or the like, the efficiency of absorption by livestock or plants will be low.
To address the aforementioned problem (1), it has been proposed to employ a vacuum dryer by way of a drying apparatus with higher capabilities (see Patent Citations 1 and 2 below, for example). However, even where organic waste drying treatment was carried out using such a vacuum dryer, the aforementioned problems (2) and (3) remained unresolved. Moreover, vacuum dryers have significant drawbacks, such as: (a) because treatment merely involves forced evaporative drying of moisture from the material being dried, complete drying does not take place, and for example if a dried product such as kitchen waste is left in an uncontrolled environment, it may reabsorb moisture and revert to its original state, with spoilage advancing as a result; and (b) vacuum drying cannot be used, for example, for highly moisture-retaining products such as seaweed (e.g. kelp) or fermented soybeans; synthetic polymer compounds in shampoos, detergents and the like; dairy products such as milk; high fat foods such as fish with high fat content; as well as products with high starch content.
Thus, as it stands currently, treatment of organic waste not only involves laborious effort, but depending on the type of organic waste, it can be difficult to treat the waste adequately to the point that it can be effectively recycled, and accordingly there exists a need for a technology whereby these problems can be resolved all at once.    Patent Citation 1: JP-A 10-85712    Patent Citation 1: JP-A 2005-221158